Activation of aluminum



Unimd v States tent ACTIVATION or Elmer H. Dobratz, Pittsburgh, Pa., assignor to Koppers Company,Inc.,-a corporation ofDelaware No Drawing. Application February 5, 1958 Serial No. 713,310

12 Claims. (Cl. 134-2) This invention relates generally to the activation of "aluminum.

'The aluminum'activated in accordance with this invention can be used in the preparation of organic compounds.

An example of such preparation is described in my copending application filed concurrently herewith. It is not intended, however, to so limit the use of the activated alu'minum, as other utilizations will lbeapparent to those skilled inthe art.

.It is .known that organo-aluminum compounds can be "formed by the direct reaction of aluminum with an olefin .and hydrogen. However, although aluminum itself is a very reactive metal, it is ordinarily covered with a very "tenaciousfilm of aluminum oxide that completely inhibits the desired reaction. Difliculty has been experienced heretofore in removing the oxide film to expose the surface of aluminum metal to attack whereupon the desired reaction will occur.

Heretofore the oxide film has been removed by milling the aluminum under a protective liquid and by spraying -molten aluminum through an inert atmosphere into a protective liquid medium. Such methods are both costly "and diflicult to operate consistently. My copending-applialkali metal and an alkaline compound of an alkaline metal is added to asuspension of comminuted aluminum in a compound having the'general formula R AlY in which R is chosen from the class consisting of hydrogen and alkyl radicals, and Y is chosen from the class con- Jsisting 'ofalkyl iradicals as a suspension medium and the suspension exposed to hydrogen, the aluminum will become activated. The function of the alkali metal or alkaline compound is not completelyunderstood, but his believed that it removes or facilitates the removal of the oxide film from the surface of the aluminum.

Suitable alkali metals and alkaline compoundso'f alkali metals include lithium, -sodium,-potassium, rubidium, and

"cesium and their oxides, hydroxides, acetates (or other carboxylates), bicarbonates, carbonates and aluminates.

Other metals such as calcium, strontium, and barium and "their alkaline'compound's are also eifectiv'e'but to a lesser Iext'ent.

The range in which the alkali metal or alkaline com- ,.pound of a metal of groups IA and HA of the periodic table has been found effective in promoting the activation of aluminum is from about 0.01% to about 10% based on the total weight of suspension medium used. Thepreferred quantity of alkali metal or alkaline compoundmis 0.05 to 0.5% of the total weight of the suspension medium used,

The activation promoter, which usually dissolves in the Patented June 30,1959

suspension medium, can be added separately or with any of the components involved in the activation.

Suitable suspension media are the'aluminum alkyls and alkyl aluminum hydridesand mixtures thereof. Those aluminum alkyls and alkyl aluminum hydrides wherein the alkyl 'groups contain from -2 to 20 carbon atoms are advantageously used in the process of this invention. The aluminum alkyls and alkyl aluminum hydrides may be used alone orin solution in aliphatic and aromatic hydrocarbons. Suitable hydrocarbons inclu-de hexane, heptane, kerosene, benzene, toluene, xylene, cyclohexane, methylcyclohexane, dimethylc'yclohex'an'e, etc. Because the use of a solvent increases the time necessary for theactivation, it is desirable that solution contain 5% or more of an aluminum alkyl or alkylaluminum hydride.

The quantity of aluminum that can be activated in a given quantity of suspension medium is limited only in that the resulting slurry must be sufliciently fluid to be stirred freely :to maintain the aluminum in suspension.

Any commercially available, comminuted aluminum can be used but so-called grained aluminum powders appear to be less-satisfactory than others. Flaked and atomized aluminum powders, such as those supplied by the Aluminum Company of America, work well. Aluminum chips .and turnings can also work well but-their low surface area makes them less desirable' from the standpoint of subsequent usage.

The process is operable at hydrogen pressures of less than '100 p.s.i. to more than 10,000 p.s.i. and-at tempera- Example I vTo an autoclave such as described above that has been thoroughly dried and purged with nitrogen or argon, there is charged 1000 parts of diethylaluminum hydride, 1000 parts of a finely comminuted commercial aluminum powder, such as Alcoa atomized aluminum powder No. 101, and 2 parts of sodium hydroxide pellets. The autoclave is then seal'ed'and hydrogen is admitted to the autoclave until a pressure of about 1000 pounds 'per'square inch is developed. The agitator is started and the autoclave and its contents are heated to C. where the pressure is adjusted to about 1500p.s.i. by admitting more hydrogen to the autoclave if necessary. The autoclave is maintained at 135 C. for a period of about five hours during which time the pressure remains essentially constant at about 1500 pounds per square inch. The aluminum has now become activated. After cooling to room temperature and venting the hydrogen, the diethylaluminum hydride may be displaced from the-aluminum with an inert liquid such as benzene or heptane under which it may be stored indefinitely without losing its activity provided it isprotectedfr'om agents such as oxygen which will destroy its activity. There remains under the sol-vent substantially 970 to 990 parts of activated aluminum. The loss'is due to mechanical losses in filteringand washing and to 'small losses due to the aluminum oxide removal.

Example 11 The process of Example I isrepeated with theex'ception that instead of 1000 parts of diethylaluminum hydride,

there is charged to the autoclave 1000 parts of di-n-propylaluminum hydride. The results are similar.

Example 111 The process of Example I is repeated with the exception that instead of 1000 parts of diethylaluminum hydride there is charged to the autoclave 1000 parts of diisobutylaluminum hydride. The results are similar.

Example IV The process of Example I is repeated with the exception that instead of 1000 parts of diethylaluminum hydride, there is charged to the autoclave 1000 parts of din-butylaluminum hydride. Similar results are obtained.

Example V The process of Example I is repeated with the exception that instead of 1000 parts of diethylaluminum hydride, there is charged 1000 parts of di-n-pentylaluminum hydride. Similar results are obtained.

Example VI To the autoclave of Example I there is charged 1000 parts of triisobutylaluminum, 1000 parts of comminuted, commercial aluminum and 1 /2 parts of sodium hydroxide pellets. The autoclave is sealed and pressurized with hydrogen to about 1000 pounds per square inch. The autoclave is heated to about 135 C. where the pressure is adjusted to about 1500 pounds per square inch by admitting more hydrogen to the autoclave if necessary. The temperature is maintained at 135 C. Within less than an hour the pressure begins to fall. Hydrogen is now admitted to the autoclave as it is required to maintain the pressure at 1500 pounds per square inch. Within three to four hours the absorption of hydrogen ceases and activation of the aluminum is complete. Upon cooling and venting the autoclave gases through a trap cooled with liquid nitrogen, there is obtained about 50-60 parts of isobutane. During the course of the activation 50-60 parts of aluminum are converted to diisobutylaluminum hydride. This loss of aluminum is off-set, however, by the increased surface of the approximately 940 parts of aluminum remaining. The increased surface results from the chemical attack in the formation of diisobutylaluminum hydride. As described in Example I, the alkyl aluminum compound can be displaced with an inert hydrocarbon to obtain the aluminum as activated aluminum for further use.

Example VII The proces of Example VI is repeated with the exception that instead of 1000 parts of triisobutylaluminum, there is utilized 1000 parts of triethylaluminum. The activation proceeds similarly. Because of lower molecular weight of triethylaluminum, approximately 100 parts of aluminum is lost in the formation of diethylaluminum hydride.

Example VIII The process of Example VI is repeated with the exception that instead of triisobutylaluminum there is utilized 1000 parts of tri-n-propylaluminum. The results are similar. The loss of aluminum in the formation of di-npropylaluminum hydride is about 80 parts.

Example IX The process of Example VI is repeated with the exception that instead of triisobutylaluminum there is utilized 1000 parts of tri-n-octylaluminum. The results are similar except that six to seven hours are required to complete the hydrogen absorption. The loss of aluminum in the formation of di-n-octylaluminum is about 30 parts.

Example X To illustrate the effects of various aluminum activation promoters, the following charge was made to the autoclave of Example I, 500 grams of diisobutylaluminum hydride, 500 grams of triisobutylaluminum, 1000 grams of a commercial, comminuted' aluminum and 0.05 grams mole of an activation promoter. The autoclave was pressurized to about 700 pounds per square inch at room temperature with hydrogen. Agitation was started and the autoclave was heated to C. where a pressure of approximately 1050 pounds per square inch developed. During the course of the activation, triisobutylaluminum was converted to diisobutylaluminum hydride. The time required to complete this reaction, which was determined by hydrogen absorption, is a relative measure of the effectiveness of the activation promoter; the shorter the period of time, the more effective is the activation promoter. By a side reaction there is formed some isobutane which is collected after completion of the activation by exhausting the gases from the autoclave through a trap cooled with liquid nitrogen in which the isobutane condenses. To effect essentially complete removal of isobutane from the autoclave the pressure on the system was finally reduced to about 25 millimeters of mercury. Generally, the more effective the activation promoter, the smaller is the quantity of isobutane obtained.

As a further check on the degree of activation and the effectiveness of the activation promoter, after completion of activation 750 grams of isobutylene was charged to the autoclave. The autoclave was pressurized to about 1000 pounds per square inch with hydrogen and heated to 135 C. where the pressure was adjusted to and maintained at 1500 pounds per square inch by admitting hydrogen to the autoclave as needed. By reaction with the activated aluminum and hydrogen, most of the isobutylene was converted to dissobutylaluminum hydride. The remainder of the isobutylene was converted to isobutane. The reaction was complete when hydrogen was no longer absorbed. Isobutane was again recovered by exhausting the gases from the autoclave through a trap cooled with liquid nitrogen. The extent of activation of the aluminum can be measured by the length of the reaction time and the quantity of isobutane formed. Short reaction time and small quantity of isobutane, for example, indicate good activation. The results obtained using a number of activation promoters are set forth in the following table.

While the foregoing description of the invention contains a limited number of specific embodiments thereof, is to be noted that the invention is limited only by the scope of the appended claims.

I claim:

1. A process for the removal of the oxide film from aluminum which has not been protected from oxidation and has become inactive to activate said aluminum, which process comprises contacting with hydrogen, aluminum which is suspended in a liquid medium selected from the group consisting of aluminum alkyls and alkyl aluminum hydrides and having therein a promoter selected from the group consisting of alkali metals and alkaline compounds of alkali metals.

2. The process of claim 1 wherein the suspension of aluminum in a liquid medium is maintained at a temperature of from 60 C. to 250 C.

3. The process of claim 1 wherein said promoter is sodium hydroxide.

4. The process of claim 1 wherein said promoter is present to the extent of 0.01% to 10% based on the total weight of suspension medium.

5. The process of claim 1 wherein said liquid medium is an alkyl aluminum compound.

6. The process of claim 1 wherein the liquid medium is about 5% of an alkyl aluminum compound in solution in a hydrocarbon.

7. The process of claim 1 which is carried out at a pressure of from 100 to 10,000 pounds per square inch.

8. The process of activating aluminum by removing the oxide film from aluminum which has become inactive because it has not been protected from oxidation which process comprises contacting hydrogen With comminuted aluminum which is in suspension in an alkyl aluminum compoud having at least 0.01% by weight of sodium hydroxide therein based on the weight of said compound and maintaining the suspension at a temperature of from 120 C. to 150 C. and under a pressure of from 1000 to 3000 pounds per square inch until the aluminum has become activated.

9. A process of activating aluminum by removing the oxide film from aluminum which has become inactive because it has not been protected from oxidation, which process comprises suspending comminuted aluminum in an alkyl aluminum compound having therein at least 0.01% by Weight of sodium hydroxide based on the weight of said compound and exposing said suspension to hydrogen for about five hours while maintaining the suspension at a temperature of from 120 C. to 150 C. and under a pressure of from 1000 to 3000 pounds per square inch whereupon the aluminum has become activated.

10. A process for the activation of aluminum by removing the oxide film from aluminum which has become inactive because it has not been protected from oxidation, comprising contacting hydrogen with inactive aluminum suspended in a compound having the formula RgAlY, in which Y is chosen from the class consisting of alkyl radicals and R is chosen from the class consisting of hydrogen and alkyl radicals and in the presence of a promoter chosen from the class consisting of a metal selected from the group consisting of lithium, so dium, potassium, rubidium, cesium, calcium, strontium and barium and alkaline compounds thereof.

11. The process of activating inactive aluminum for use in organic synthesis by removing the oxide film from said inactive aluminum, comprising contacting with hydrogen comminuted aluminum which is slurried in a compound having the formula R A1Y in which Y is chosen from the class consisting of alkyl radicals and R is chosen from the class consisting of hydrogen and alkyl radicals, said compound having in solution therein at least 0.01% by weight of sodium hydroxide based on the weight of said compound, said contact being effected at a temperature of from C. to 150 C. and at a pressure of from 10003000 pounds per square inch until the aluminum becomes activated, thereafter cooling the suspension to room temperature, decreasing the pressure to atmospheric pressure, and displacing said compound with an inert liquid which is free of oxygen whereby the activated aluminum may be kept indefinitely in its activated state.

12. A process for activating inactive comminuted aluminum by removing the oxide film from said inactive aluminum which comprises adding said liquid inactive aluminum to a liquid compound having the general formula R AlY in which Y is chosen from the class consisting of alkyl radicals having from two to twenty carbon atoms and R is chosen from the class consisting of hydrogen and alkyl radicals having from two to twenty carbon atoms to form a slurry that is thin enough to maintain the aluminum in suspension in the liquid by agitation, adding to said slurry about 0.05 to 0.5% of sodium hydroxide based on the weight of said compound, placing said slurry in contact with hydrogen and under a hydrogen pressure of about 1000 pounds per square inch at room temperature, agitating said slurry while heating to about C., adjusting the hydrogen pressure to about 1500 pounds per square inch and maintaining the hydrogen and slurry contact at the latter temperature and pressure for about five hours, and thereafter displacing said liquid compound from the aluminum with an inert oxygen-free liquid hydrocarbon whereby the aluminum may be kept under the hydrocarbon indefinitely without losing its activity so long as the inert liquid protects the activated aluminum from agents such as oxygen which destroys its activity.

References Cited in the file of this patent UNITED STATES PATENTS 2,843,474 Ziegler et al. July 15, 1958 FOREIGN PATENTS 535,235 Belgium Feb. 15, 1955 

1. A PROCESS FOR THE REMOVAL OF THE OXIDE FILM FROM ALUMINUM WHICH HAS NOT BEEN PROTECTED FROM OXIDATION AND HAS BECOME INACTIVE TO ACTIVATE SAID ALUMINUM, WHICH PROCESS COMPRISES CONTACTING WITH HYDROGEN, ALUMINUM WHICH IS SUSPENDED IN A LIQUID MEDIUM SELECTED FROM THE GROUP CONSISTING OF ALUMINUM ALKYLS AND ALKYL ALUMINUM HYDRIDES AND HAVING THEREIN A PROMOTER SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS AND ALKALINE COMPOUNDS OF ALKALI METALS. 